It is common practice in gold or platinum mining and exploration operations to assay the ore in order to quantify the amount of gold and/or PGM's (platinum, palladium, rhodium, osmium, iridium and ruthenium) present.
The conventional assaying process is commonly known as “fire assay”. The process involves weighing an amount of a comminuted ore, and mixing it with a lead oxide bearing flux or nickel flux. The mixture is then placed in a crucible and heated to elevated temperatures usually around 1100 to 1250 degrees Celsius for a period of about 60 to 90 minutes.
During this process the mixture melts, the lead oxide is reduced to lead metal or nickel sulfide is formed and the lead or nickel sulfide acts to collect the PGM's and/or gold due to their chemical affinity.
The molten slag and collector material is poured in to a mould where it is allowed to cool. The lead or nickel sulfide settles to the bottom of the mould. Once the mould is cooled, the lead or nickel sulfide is separated from the slag using mechanical techniques. The procedure is labour intensive. Once the collector material has been separated from the slag, it is placed in a cupel which is pre-heated at 1000 to 1300 degrees Celsius to allow the lead to be absorbed by the cupel. The result is a tiny prill left at the base of the cupel. The PGM's and gold content in the prill can then be determined using a number of analytical techniques.
Apart from the time consuming process described above, it has been found that during the loading and removal of reaction vessels or crucibles from a fire assay furnace considerable energy losses occur resulting in further delays in the assaying process.
Regarding the fluxes used in fire assay processes, conventional components of fluxes include borax (hydrated sodium borate), sodium carbonate, litharge (lead monoxide), silica, carbon, fluospar, red lead Pb3O4) potassium nitrate, and iron.